Police are increasingly being targeted by Taliban fighters as Afghan security forces take greater responsibility for security before NATO troops withdraw in 2014.

Roadside bombs, either remotely-controlled or weight-detonated, are weapons that the Taliban have used often.

Helicopter crash

Meanwhile, in the eastern Kapisa province, a NATO helicopter crashed on Thursday, but no crew members were seriously injured, officials said.

Taliban spokesman Zabiullah Mujahid claimed the helicopter was shot down by the group's fighters in the Tagab district of Kapisa province.

A spokesman for US-led forces in the country said the cause of the crash is still being investigated.

"Both members of the helicopter crew were recovered from the crash and neither was seriously injured," US Army Major Adam Wojack said. "We do not yet have definitive information on whether or not enemy activity was present in the area at the time of the crash."

In an earlier statement, the International Security Assistance Force, as the US-led military coalition in Afghanistan is known, said the site of the crash had been secured. It did not provide a location or other details.